A basic development direction of portable Internet should be focused on faster data communication. Since it is difficult to further improve the portable Internet through a frequency bandwidth that is already nearing semi-saturation, a MIMO mechanism, which increases frequency efficiency using spatial division, will be used as a main mechanism in next-generation mobile communication.
A mobile communication system using the MIMO mechanism transmits data through independent channels that are formed among MIMO antennas of transmitting and receiving ends, thereby making it possible to obtain a data transmission rate that is higher than a system using a single antenna.
In the MIMO system, assuming that the transmitting end or the receiving end knows the information of the channels, the interference signals can be removed by a proper detection mechanism or a precoding mechanism.
The MIMO system can be applied to a cellular system that simultaneously supports multiple users. At this time, since cooperation communication between terminals cannot be generally performed, a base station transmits data to not cause inter-user interference using the precoding mechanism in a downlink.
In the MIMO system supporting multiple users, the mechanism to remove the inter-user interference depends on a dirty paper coding mechanism. The paper coding mechanism can completely remove the inter-user interference without losing transmittable data, but cannot be realistically implemented due to its complexity. Therefore, as an actual mechanism applied to remove the inter-user interference, a simplified nonlinear mechanism such as the Tomlinson Harashima precoder (THP) or a linear mechanism such as block diagonalization has been used.
The block diagonalization mechanism is relatively simple and shows good error performance, but has a drawback of a large loss of channel capacity as the number of users that are simultaneously supported increases. However, the THP mechanism has an advantage in that the loss of channel capacity is small even though the number of users increases, but has a disadvantage in that the system complexity is large and the error performance is degraded when there are a relatively small number of users.
Examples of mechanisms to improve the above-mentioned disadvantages of the block diagonalization or the THP may include a BTHP mechanism to remove the inter-user interference and a maximum likelihood (ML) receiving mechanism designed to be suitable therefore so as to improve the error performance of the THP using the MIMO antennas of the user.
The BTHP mechanism using the ML shows excellent error performance as compared to the existing THP mechanism, but still has a disadvantage in that the error performance is degraded as compared to the block diagonalization mechanism using the ML.
Therefore, a need exists for an additional optimization mechanism in order to further improve the error performance of the BTHP mechanism using the MLS.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.